Hybrid automotive powertrain system and method of operating same

ABSTRACT

A hybrid powertrain system for a vehicle includes an electric machine, a gear set mechanically connected with the electric machine, and a clutch mechanically coupled with at least one of a primary and secondary driveline assembly. The electric machine is configured to selectively provide motive power to at least one of the primary and secondary driveline assemblies. The gear set is configured to permit differential rotation between the primary and secondary driveline assemblies. The clutch is configured to selectively transfer torque between the primary and secondary driveline assemblies.

BACKGROUND

1. Field of the Invention

The invention relates to hybrid automotive powertrain systems andmethods of operating the same.

2. Discussion

Drivetrains for hybrid automotive vehicles may be configured andoperated in several ways. As an example, U.S. Pat. No. 5,993,351 toDeguchi et al. discloses a first electrical motor mechanically connectedto an engine and a second electrical motor mechanically connected to theengine through a clutch. Motive force is transmitted from the secondelectrical motor to drive wheels through a transmission. It is decidedwhether to release the clutch based on a detected vehicle speed and adetected required motive force. Engine output at that time is estimated.The second electrical motor is controlled such that generated torquecorresponds to the estimated engine output if it is decided to releasethe clutch. The first electrical motor is controlled such that thetorque generated by the second electrical motor is absorbed.

As another example, U.S. Pat. No. 6,041,877 to Yamada et al. discloses adrive unit for a hybrid vehicle. The drive unit includes an internalcombustion engine, a transmission connected to the internal combustionengine via a clutch and a primary differential gear for distributing adriving force transmitted from the transmission to primary drivingwheels. The drive unit also includes a transfer connected to the primarydifferential gear for taking out a part of the driving force transmittedfrom the transmission to the primary differential gear, a pair ofpropeller shafts for transmitting part of the driving force from thetransfer to a secondary differential gear, and an electric motorprovided between the propeller shafts. The drive unit further includes apair of clutches, each connecting the electric motor to one of the pairof propeller shafts.

As yet another example, U.S. Pat. No. 6,190,282 to Deguchi et al.discloses a first electric motor connected mechanically to an engine anda second electric motor connected mechanically through a clutch to theengine. Drive force is transmitted to drive wheels through atransmission from the second electric motor. It is decided whether toconnect the clutch on the basis of driving conditions. The engine iscontrolled so that the output of the engine meets the required forcewhen it is decided to connect the clutch. The first electric motorfunctions as an electric generator such that the rotation speed of theengine reaches a target rotation speed. The clutch is connected when theengine is rotating at a target rotation speed.

SUMMARY

A hybrid powertrain system for a vehicle includes a clutch mechanicallycoupled with at least one of a primary driveline assembly and secondarydriveline assembly, an electric machine and a gear set mechanicallyconnected with the electric machine. The clutch is configured toselectively transfer torque between the primary driveline assembly andsecondary driveline assembly. The electric machine is configured toselectively provide motive power to at least one of the primarydriveline assembly and secondary driveline assembly. The gear set isconfigured to permit differential rotation between the primary drivelineassembly and secondary driveline assembly.

A method for operating a power transfer box of an automotive hybridpowertrain includes providing motive power to at least one of a primarydriveline assembly and secondary driveline assembly by convertingelectrical power to motive power, transferring torque between thesecondary driveline assembly and primary driveline assembly via a clutchand transferring torque between the secondary driveline assembly andprimary driveline assembly via a gear set.

While example embodiments in accordance with the invention areillustrated and disclosed, such disclosure should not be construed tolimit the invention. It is anticipated that various modifications andalternative designs may be made without departing from the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of a powertrain systemfor an automotive vehicle.

FIG. 2 is a schematic diagram of the electric front/rear auxiliary driveof FIG. 1.

FIG. 3 is a schematic diagram of another embodiment of an electricfront/rear auxiliary drive.

FIG. 4 is a schematic diagram of yet another embodiment of an electricfront/rear auxiliary drive.

FIG. 5 is a schematic diagram of still yet another embodiment of anelectric front/rear auxiliary drive.

DETAILED DESCRIPTION

Referring now to FIG. 1, a hybrid electric vehicle 10 may include anengine 12, crank machine 14, transaxle 16 and power transfer unit 18.The vehicle 10 may also include a front prop shaft 20, rear prop shaft22, electric front/rear auxiliary drive (EFRAD) 24, high voltage battery26 and power electronics 28. The vehicle 10 may further include left andright front half-shafts 30, 32, rear axle assembly 34, left and rightrear half-shafts 36, 38 and wheel and tire assemblies 40, 42, 44, 46.The operation of these elements will be described in greater detailbelow.

In other embodiments, the vehicle 10 may have a north-south powertrainconfiguration and/or a fewer or greater number of electric machines. Ofcourse, other vehicle configurations are also possible.

As apparent to those of ordinary skill, elements shown adjacent to oneanother are mechanically coupled. As an example, the crank machine 14 ismechanically coupled with the engine 12 and transaxle 16 via, forexample, suitable gearing. As another example, the rear axle assembly 34is mechanically coupled with the left and right rear half-shafts 36, 38and rear prop shaft 22 via, for example, suitable gearing. Torque maythus be transferred between the engine 12 and/or crank machine 14 andthe EFRAD 24 via the transaxle 16, power transfer unit 18 and front propshaft 20. Likewise, torque may be transferred between the rear axleassembly 34 and the EFRAD 24 via the rear prop shaft 22, etc.

Certain embodiments of the EFRAD 24, as explained in detail below, mayselectively transfer torque to, from and/or between the front and rearprop shafts 20, 22. Certain embodiments of the EFRAD 24 may alsoselectively convert between motive power and electrical power.

Referring now to FIGS. 1 and 2, an electric machine 48 includes a stator50 and rotor 52. The electric machine 48 may provide electrical powerto, or receive electrical power from, the high voltage battery 26 viathe power electronics 28. The stator 50 is fixedly attached, e.g.,bolted, with a housing (not shown) of the EFRAD 24. The rotor 52 isrotatably located, e.g. via bearings, within a housing (not shown) andabout a linking shaft 54. The linking shaft 54 and the front prop shaft20 are connected via a joint 55. The rotor 52 thus rotates relative tothe front prop shaft 22. As apparent to those of ordinary skill, otherarrangements and configurations are also possible.

A planetary gear set 58 includes a sun gear 60, planet gears 62 and ringgear 64. The sun gear 60 is fixedly attached, e.g., press fit, with aleg portion 66 of the rotor 52. The sun gear 60 thus rotates with thefront prop shaft 20. In other embodiments, any suitable gear set, e.g.,parallel axis, hypoid, spiral bevel, etc., may be used. As apparent tothose of ordinary skill, the use of certain gear sets may require, forexample, the electric machine 48 to be repositioned within the EFRAD 24,etc.

An inner carrier 68 is fixedly attached, e.g., press fit, with thelinking shaft 54. The inner carrier 68 carries the planet gears 62 andinner clutches 70 of the clutch pack 56. The planet gears 62 and innerclutches 70 thus rotate with the front prop shaft 20.

An outer carrier 72 is connected with the rear prop shaft 22 via a joint74. The outer carrier 72 carries the ring gear 64 and outer clutches 76of the clutch pack 56. The ring gear 64 and outer clutches 76 thusrotate with the rear prop shaft 22.

In other embodiments, inner clutches and outer clutches may be carriedby any suitable component. For example, outer clutches may be carried bya leg portion of a rotor or an outer carrier. Inner clutches may becarried by a leg portion of a rotor. Other configurations are alsopossible.

In a first mode of operation, the engine 12 produces torque andtransmits it to the driveline. The electric machine 48 is disabled, andtherefore provides no reaction torque to the planet gears 62 via the sungear 60. As a result, no torque is transferred from the planet gears 62to the rear prop shaft 22 via the ring gear 64. The clutch pack 56 isnot compressed. As a result, no torque is transferred from the linkingshaft 54 to the rear prop shaft 22 via the clutch pack 56. Note thattorque from the engine 12 is also being applied to the wheel and tireassemblies 40, 42 through the power transfer unit 18 and fronthalf-shafts 30, 32.

In a second mode of operation, the engine 12 produces torque andtransmits it to the driveline.

Electrical power is produced by the electric machine 48 and is sent tothe power electronics 28 to be stored in the high voltage battery 26 orused for other purposes. The electric machine 48, therefore, appliesreaction torque to the planet gears 62 via the sun gear 60. As a result,torque is transferred from the planet gears 62 to the rear prop shaft 22via the ring gear 64. The clutch pack 56 is not compressed. As a result,no torque is transferred from the linking shaft 54 to the rear propshaft 22 via the clutch pack 56. The torque from the rear prop shaft 22is transferred to the left and right rear half-shafts 36, 38 via therear axle assembly 34 to drive the wheel and tire assemblies 44, 46.

In this mode of operation, the electric machine 48 behaves as agenerator. If the mechanical power applied by the electric machine 48 is−x and the mechanical power applied by the front prop shaft 20 is y, themechanical power transferred to the rear prop shaft 22 is the sum of −xand y (less any system losses.) If the electric machine 48 behaves as amotor, the mechanical power transferred to the rear prop shaft 22 is thesum of x and y (less any system losses.)

In a third mode of operation, no engine torque is being transmitted tothe driveline. Electrical power from the power electronics 28 isprovided to the electric machine 48. The electric machine 48, therefore,applies torque to the planet gears 62 via the sun gear 60, andconsequently to the ring gear 64 via the planet gears 62. As a result,torque is transferred to the front prop shaft 20 via the planet gears 62and to the rear prop shaft 22 via the ring gear 64. The clutch pack 56is not compressed. As a result, no torque is transferred between thelinking shaft 54 and the rear prop shaft 22 via the clutch pack 56. Thetorque from the front prop shaft 20 is transferred to the left and rightfront half-shafts 30, 32 via the power transfer unit 18 to drive thewheel and tire assemblies 40, 42. The torque from the rear prop shaft 22is transferred to the left and right rear half-shafts 36, 38 via therear axle assembly 34 to drive the wheel and tire assemblies 44, 46.

In this mode of operation, the electric machine 48 behaves as a motor.The mechanical power from the machine 48 is distributed between thefront prop shaft 20 and rear prop shaft 22, and the amount to each is afunction of the driveline gear ratios, including that of the planetarygear set 58 (less any system losses.) If the electric machine 48 behavesas a generator, the mechanical power absorbed by the electric machine 48from the front prop shaft 20 and rear prop shaft 22 is also a functionof the driveline gear ratios (less any system losses.)

In a fourth mode of operation, the engine 12 produces torque andtransmits it to the driveline. The electric machine 48 is disabled, andtherefore provides no torque to the planet gears 62 via the sun gear 60.As a result, no torque is transferred from the planet gears 62 to therear prop shaft 22. The clutch pack 56 is compressed to variablytransfer torque from the linking shaft 54 to the rear prop shaft 22. Thetorque from the rear prop shaft 22 is transferred to the left and rightrear half-shafts 36, 38 via the rear axle assembly 34 to drive the wheeland tire assemblies 44, 46. Note that torque from the engine 12 is alsobeing applied to the front wheel and tire assemblies 40, 42 through thepower transfer unit 18 and front half-shafts 30, 32.

In a fifth mode of operation, the engine 12 produces torque andtransmits it to the driveline.

Electrical power is produced by the electric machine 54 and is sent tothe power electronics 28 to be stored in the high voltage battery 26 orused for other purposes. The electric machine 48, therefore, appliesreaction torque to the planet gears 62 via the sun gear 60. As a result,torque is transferred from the planet gears 62 to the rear prop shaft 22via the ring gear 64. The clutch pack 56 is compressed to variablytransfer torque from the linking shaft 54 to the rear prop shaft 22. Thetorque from the rear prop shaft 22 is transferred to the left and rightrear half-shafts 36, 38 via the rear axle assembly 34 to drive the wheeland tire assemblies 44, 46. Note that torque from the engine 12 is alsobeing applied to the front wheel and tire assemblies 40, 42 through thepower transfer unit 18 and the front half-shafts 30, 32.

In this mode of operation, the electric machine 48 behaves as agenerator. The mechanical power transferred to the rear prop shaft 22 isa function of the mechanical power absorbed by the machine 48 and theamount of clutch pack 56 engagement (less any system losses.) If theelectric machine 48 behaves as a motor, the mechanical power applied tothe rear prop shaft 22 is a function of the mechanical power applied bythe machine 48 and the amount of clutch pack 56 engagement (less anysystem losses.)

In a sixth mode of operation, no engine torque is being transmitted tothe driveline. Electrical power from the power electronics 28 isprovided to the electric machine 48. The electric machine 48, therefore,applies torque to the planet gears 62 via the sun gear 60, andconsequently to the ring gear 64 via the planet gears 62. As a result,torque is transferred to the front prop shaft 20 via the planet gears 62and to the rear prop shaft 22 via the ring gear 64. The clutch pack 56is compressed to variably transfer torque between the linking shaft 54to the rear prop shaft 22, for example, to limit differentiation betweenthe front and rear prop-shafts 20, 22. The torque from the front propshaft 20 is transferred to the left and right front half-shafts 30, 32via the power transfer unit 18 to drive the wheel and tire assemblies40, 42. The torque from the rear prop shaft 22 is transferred to theleft and right rear half-shafts 36, 38 via the rear axle assembly 34 todrive the wheel and tire assemblies 44, 46.

In this mode of operation, the electric machine 48 behaves as a motor.The mechanical power from the electric machine 48 is distributed betweenthe front prop shaft 20 and rear prop shaft 22, and the amount to eachis a function of the driveline gear ratios, including that of theplanetary gear set 58, and the amount of clutch pack 56 engagement (lessany system losses.) If the electric machine 48 behaves as a generator,the mechanical power absorbed by the electric machine 48 from the frontprop shaft 20 and rear prop shaft 22 is also a function of the drivelinegear ratios and the amount of clutch pack 56 engagement (less any systemlosses).

The clutch pack 56 may provide variable front/rear torque biasing forregenerative braking and propulsion. As an example, the torque biasingrelative to the electric machine 48 may be 50% front and 50% rear whenthe clutch pack 56 is fully compressed and allowing no speeddifferentiation between front prop shaft 20 and rear prop shaft 22. Asanother example, the torque biasing relative to the electric machine 48may be 70% front and 30% rear when the clutch pack 56 is not compressedand the planetary gear set ratio provides a 70/30 front/rear torquesplit. In some embodiments, variable clutch pack engagement permitsvariable front/rear torque biasing from 50% front and 50% rear to 70%front and 30% rear. Other biasing schemes, however, are also possible,e.g., 90/10, 40/60, etc.

Referring to FIG. 3, numbered elements of FIG. 3 that differ by 100relative to the numbered elements of 2 have similar, although notnecessarily identical, descriptions to the numbered elements of FIG. 2.In this embodiment, however, the EFRAD 124 has a configuration that isthe reverse of that illustrated in FIG. 2. That is, the linking shaft154 is connected with the rear prop shaft 122 via the joint 174, and theouter carrier 172 is connected with the front prop shaft 120 via thejoint 155.

As apparent to those of ordinary skill, the operation of the EFRAD 124is similar to that of the EFRAD 24 illustrated in FIG. 2 taking intoaccount its reverse configuration. The EFRAD 124, however, provides theopposite front/rear torque split relative to the EFRAD 24 illustrated inFIG. 1. If, for example, the EFRAD 24 illustrated in FIG. 1 provides anarrangement with a 70/30 front/rear torque split, a reverse of thatarrangement would provide a 30/70 front/rear torque split, etc.

Referring to FIG. 4, numbered elements of FIG. 4 that differ by 200relative to the numbered elements of 2 have similar, although notnecessarily identical, descriptions to the numbered elements of FIG. 2.In this embodiment, however, the outer carrier 272 does not carry thering gear 264. Rather, the ring gear 264 is fixedly attached, e.g.,bolted, with a housing (not shown) of the EFRAD 224. In otherembodiments, any suitable gear set, e.g., parallel axis, hypoid, spiralbevel, etc., may be used. As apparent to those of ordinary skill, theuse of certain gear sets may require, for example, the electric machine248 to be repositioned within the EFRAD 224, etc.

In a first mode of operation, an engine (not shown) produces torque andtransmits it to the driveline. The electric machine 248 is disabled, andtherefore provides no reaction torque to the planet gears 262 via thesun gear 260. As a result, no torque is transferred to or from the frontprop shaft 220 via the planet gears 262. The clutch pack 256 is notcompressed. As a result, no torque is transferred from the linking shaft254 to the rear prop shaft 222 via the clutch pack 256.

In a second mode of operation, the engine (not shown) produces torqueand transmits it to the driveline. Electrical power is produced by theelectric machine 248 and is sent to power electronics (not shown) to bestored in a high voltage battery (not shown) or used for other purposes.The electric machine 248, therefore, applies reaction torque to theplanet gears 262 via the sun gear 260. As a result, torque produced bythe engine is converted into electrical power. The clutch pack 56 is notcompressed. As a result, no torque is transferred from the linking shaft254 to the rear prop shaft 222 via the clutch pack 256.

In this mode of operation, the electric machine 248 behaves as agenerator. If the electric machine 248 behaves as a motor, torquetransmitted to the driveline is the sum of engine torque and electricmachine torque (minus other loads and system losses).

In a third mode of operation, no engine torque is being transmitted tothe driveline. Electrical power from the power electronics (not shown)is provided to the electric machine 248. The electric machine 48,therefore, applies torque to the planet gears 262 via the sun gear 260.As a result, torque is transferred to the front prop shaft 220 via theplanet gears 262. The clutch pack 256 is not compressed. As a result, notorque is transferred between the linking shaft 254 and the rear propshaft 222 via the clutch pack 256.

In this mode of operation, the electric machine 248 behaves as a motor.If machine 248 behaves as a generator, mechanical power absorbed by theelectric machine 248 from the front prop shaft 220 is converted toelectrical power.

In a fourth mode of operation, the engine (not shown) produces torqueand transmits it to the driveline. The electric machine 248 is disabled,and therefore provides no torque to the planet gears 262 via the sungear 260. As a result, no torque is transferred to or from the frontprop shaft 220 via the planet gears 262. The clutch pack 256 iscompressed to variably transfer torque from the linking shaft 254 to therear prop shaft 222.

In a fifth mode of operation, the engine (not shown) produces torque andtransmits it to the driveline. Electrical power is produced by theelectric machine 254 and is sent to the power electronics (not shown) tobe stored in the high voltage battery (not shown) or used for otherpurposes. The electric machine 248, therefore, applies reaction torqueto the planet gears 262 via the sun gear 260. As a result, torqueproduced by the engine (not shown) is converted into electrical power.The clutch pack 256 is compressed to variably transfer torque from thelinking shaft 254 to the rear prop shaft 222.

In this mode of operation, the electric machine 248 behaves as agenerator. If the electric machine 248 behaves as a motor, torquetransmitted to the driveline is the sum of engine torque and electricmachine torque (minus other loads and system losses).

In a sixth mode of operation, no engine torque is being transmitted tothe driveline. Electrical power from the power electronics (not shown)is provided to the electric machine 248. The electric machine 248,therefore, applies torque to the planet gears 262 via the sun gear 260.As a result, torque is transferred to the front prop shaft 220 via theplanet gears 262. The clutch pack 256 is compressed to variably transfertorque between the linking shaft 254 and the rear prop shaft 222.

In this mode of operation, the electric machine 248 behaves as a motor.If the electric machine 248 behaves as a generator, mechanical powerabsorbed by the electric machine 248 from the front prop shaft 220 andrear prop shaft 222 is converted to electrical power.

The clutch pack 256 may provide variable front/rear torque biasing forregenerative braking and propulsion. As an example, the torque biasingmay be 50% front and 50% rear when the clutch pack 256 is fullycompressed and allowing no speed differentiation between front propshaft 220 and rear prop shaft 222. As another example, the torquebiasing may be 100% front when the clutch pack 256 is not compressed. Insome embodiments, variable clutch pack engagement allows for variablefront/rear torque biasing from 50% front and 50% rear to 100% front.

Referring now to FIG. 5, numbered elements of FIG. 5 that differ by 100relative to the numbered elements of 4 have similar, although notnecessarily identical, descriptions to the numbered elements of FIG. 5.In this embodiment, however, the EFRAD 324 has a configuration that isthe reverse of that illustrated in FIG. 4. That is, the linking shaft354 is connected with the rear prop shaft 322 via the joint 374, and theouter carrier 372 is connected with the front prop shaft 320 via thejoint 355.

As apparent to those of ordinary skill, the operation of the EFRAD 324is similar to that of the EFRAD 224 illustrated in FIG. 4 taking intoaccount its reverse configuration. The EFRAD 324, however, provides theopposite front/rear torque split relative to the EFRAD 324 illustratedin FIG. 4.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. A hybrid powertrain system for a vehicle comprising: a clutchmechanically coupled with at least one of a primary driveline assemblyand secondary driveline assembly and configured to selectively transfertorque therebetween; an electric machine configured to selectivelyprovide motive power to at least one of the primary driveline assemblyand secondary driveline assembly; and a gear set mechanically connectedwith the electric machine and configured to permit differential rotationbetween the primary driveline assembly and secondary driveline assembly.2. The system of claim 1 wherein the electric machine is furtherconfigured to selectively convert motive power received from at leastone of the primary driveline assembly and secondary driveline assemblyto electrical power.
 3. The system of claim 1 wherein the electricmachine is further configured to selectively free spin.
 4. The system ofclaim 1 wherein the gear set includes a first element mechanicallyconnected with the electric machine.
 5. The system of claim 4 whereinthe gear set further includes a second element mechanically connectedwith one of the primary driveline assembly and secondary drivelineassembly.
 6. The system of claim 5 wherein the gear set comprises anepicyclic gear set and wherein the epicyclic gear set further includes athird element mechanically connected with the other of the primarydriveline assembly and secondary driveline assembly.
 7. The system ofclaim 1 wherein the clutch is further configured to vary the torquetransfer between the primary driveline assembly and secondary drivelineassembly.
 8. The system of claim 1 wherein the vehicle further includesan energy storage unit and wherein the electric machine is furtherconfigured to provide electrical power to the energy storage unit. 9.The system of claim 1 wherein the vehicle further includes an energystorage unit and wherein the electric machine is further configured toreceive electrical power from the energy storage unit.
 10. An automotivehybrid powertrain system for a vehicle including a primary drivelineassembly and secondary driveline assembly, the system comprising: apower transfer box including an electric machine, a gear setmechanically connected with the electric machine, and a clutchmechanically coupled with at least one of the primary driveline assemblyand secondary driveline assembly, the power transfer box beingconfigured to selectively (i) provide motive power to at least one ofthe primary driveline assembly and secondary driveline assembly byconverting electrical power to motive power, (ii) convert motive powerreceived from at least one of the primary driveline assembly andsecondary driveline assembly to electrical power, (iii) transfer torquebetween the secondary driveline assembly and primary driveline assemblyvia the clutch, (iv) transfer torque between the secondary drivelineassembly and primary driveline assembly via the gear set, and (v)transfer torque between the electric machine and at least one of theprimary driveline assembly and secondary driveline assembly via the gearset.
 11. The system of claim 10 wherein the power transfer box isfurther configured to permit differential rotation between the secondarydriveline assembly and primary driveline assembly.
 12. The system ofclaim 10 wherein the gear set includes a first element mechanicallyconnected with the electric machine.
 13. The system of claim 12 whereinthe gear set includes a second element mechanically connected with oneof the primary driveline assembly and secondary driveline assembly. 14.The system of claim 13 wherein the gear set comprises an epicyclic gearset and wherein the epicyclic gear set includes a third elementmechanically connected with the other of the primary driveline assemblyand secondary driveline assembly.
 15. The system of claim 10 wherein thevehicle further includes an energy storage unit and wherein the electricmachine is further configured to provide electrical power to the energystorage unit.
 16. The system of claim 10 wherein the vehicle furtherincludes an energy storage unit and wherein the electric machine isfurther configured to receive electrical power from the energy storageunit.
 17. A method for operating a power transfer box of an automotivehybrid powertrain, the method comprising: providing motive power to atleast one of a primary driveline assembly and secondary drivelineassembly by converting electrical power to motive power; transferringtorque between the secondary driveline assembly and primary drivelineassembly via a clutch; and transferring torque between the secondarydriveline assembly and primary driveline assembly via a gear set. 18.The method of claim 17 further comprising converting motive powerreceived from at least one of the primary driveline assembly andsecondary driveline assembly to electrical power.
 19. The method ofclaim 17 further comprising transferring torque between an electricmachine and at least one of the primary driveline assembly and secondarydriveline assembly via the gear set.
 20. The method of claim 17 furthercomprising permitting differential rotation between the secondarydriveline assembly and primary driveline assembly.
 21. The method ofclaim 17 further comprising providing electrical power to an energystorage unit.
 22. The method of claim 17 further comprising receivingelectrical power from an energy storage unit.
 23. An automotive hybridpowertrain system comprising: an electric machine configured toselectively provide motive power to at least one of a primary drivelineassembly and secondary driveline assembly by converting electrical powerto motive power; an epicyclic gear set including a sun gear mechanicallyconnected with the electric machine, at least one planet gearmechanically coupled with one of the primary driveline assembly andsecondary driveline assembly and a non-rotating ring gear; and a clutchmechanically coupled with at least one of the primary driveline assemblyand secondary driveline assembly and configured to selectively transfertorque between the primary driveline assembly and secondary drivelineassembly.
 24. The system of claim 23 wherein the electric machine isfurther configured to selectively convert motive power received from atleast one of the primary driveline assembly and secondary drivelineassembly to electrical power.
 25. The system of claim 23 wherein theelectric machine is further configured to selectively free spin.
 26. Thesystem of claim 23 wherein the clutch is further configured to vary thetorque transfer between the primary driveline assembly and secondarydriveline assembly.
 27. The system of claim 23 wherein the electricmachine is further configured to provide electrical power to an energystorage unit.
 28. The system of claim 23 wherein the electric machine isfurther configured to receive electrical power from an energy storageunit.
 29. A hybrid powertrain system for a vehicle including a primarydriveline assembly and secondary driveline assembly, the systemcomprising: a power transfer box including an electric machine, a clutchmechanically coupled with at least one of the primary driveline assemblyand secondary driveline assembly, and a gear set including a firstelement mechanically connected with the electric machine and a secondelement mechanically coupled with one of the primary driveline assemblyand secondary driveline assembly, the power transfer box beingconfigured to selectively (i) provide motive power to at least one ofthe primary driveline assembly and secondary driveline assembly byconverting electrical power to motive power via the electric machine,and (ii) transfer torque between the secondary driveline assembly andprimary driveline assembly via the clutch.
 30. The system of claim 29wherein the power transfer box is further configured to selectivelytransfer torque between the electric machine and at least one of theprimary driveline assembly and secondary driveline assembly.
 31. Thesystem of claim 29 wherein the power transfer box is further configuredto convert motive power received from at least one of the primarydriveline assembly and secondary driveline assembly to electrical powervia the electric machine.
 32. The system of claim 29 wherein the gearset comprises an epicyclic gear set and wherein the epicyclic gear setincludes a non-rotating third element.